U.S. patent application number 10/596763 was filed with the patent office on 2009-10-01 for zoom optical system.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONIC, N.V.. Invention is credited to Bernardus Hendrikus Wilhelmus Hendriks, Stein Kuiper.
Application Number | 20090244718 10/596763 |
Document ID | / |
Family ID | 32116384 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090244718 |
Kind Code |
A1 |
Hendriks; Bernardus Hendrikus
Wilhelmus ; et al. |
October 1, 2009 |
ZOOM OPTICAL SYSTEM
Abstract
A zoom optical system is provided which has a lens system which
comprises a first lens which is arranged to provide a continuously
variable focus for a beam of radiation. The lens system further
comprises a switchable optical element including a first fluid, a
second fluid and a wavefront modifier having a part through which
said radiation beam is arranged to pass. In a first mode the
switchable optical element has a first fluid configuration with
said part being substantially covered by the first fluid, and in a
second mode the switchable optical element has a second, different,
fluid configuration with said part being substantially covered by
the second fluid.
Inventors: |
Hendriks; Bernardus Hendrikus
Wilhelmus; (Eindhoven, NL) ; Kuiper; Stein;
(Eindhoven, NL) |
Correspondence
Address: |
PHILIPS INTELLECTUAL PROPERTY & STANDARDS
P.O. BOX 3001
BRIARCLIFF MANOR
NY
10510
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONIC,
N.V.
EINDHOVEN
NL
|
Family ID: |
32116384 |
Appl. No.: |
10/596763 |
Filed: |
January 4, 2005 |
PCT Filed: |
January 4, 2005 |
PCT NO: |
PCT/IB2005/050028 |
371 Date: |
June 23, 2006 |
Current U.S.
Class: |
359/666 |
Current CPC
Class: |
G02B 15/00 20130101;
G02B 26/005 20130101; G02B 3/14 20130101 |
Class at
Publication: |
359/666 |
International
Class: |
G02B 3/14 20060101
G02B003/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2004 |
EP |
04100025.8 |
Claims
1. A zoom optical system comprising a lens system which is arranged
to provide a variable zoom setting for a beam of radiation, wherein
the lens system comprises a switchable optical element having a
first mode and a second mode, characterised in that the element
includes a first fluid, a second fluid and a wavefront modifier
having a part through which said radiation beam is arranged to
pass, wherein in the first mode the switchable optical element has
a first fluid configuration in which said part is substantially
covered by the first fluid, and in the second mode the switchable
optical element has a second, different, fluid configuration in
which said part is substantially covered by the second fluid
2. A zoom optical system according to claim 1, wherein the first
fluid is a liquid and the second fluid is gaseous.
3. A zoom optical system according to claim 1, wherein the
switchable optical element comprises a common first fluid
electrode, a second, different, fluid electrode and a third,
different, fluid electrode, wherein in the first fluid
configuration the element is arranged to provide switchable
electrowetting forces by applying a first voltage across said first
and second fluid electrodes, and in the second fluid configuration
the element is arranged to provide different switchable
electrowetting forces by applying a second, different, voltage
across said first and third fluid electrodes.
4. A zoom optical system according to claim 1, wherein the
switchable optical element comprises a further wavefront modifier
having a different part through which said radiation beam is
arranged to pass, wherein the wavefront modifier is adapted to
perform a first wavefront modification and the further wavefront
modifier is adapted to perform a second, different, wavefront
modification which is arranged to complement the first wavefront
modification.
5. A zoom optical system according to claim 1, wherein the
wavefront modifier has a face, wherein said face is substantially
spherical or aspherical, and said part is on said face.
6. A zoom optical system according to claim 1, wherein said first
lens is a fluid meniscus lens which comprises different fluids
separated by a fluid meniscus having a curvature, wherein the
optical system further comprises a control system and the variable
focus comprises variations in the fluid meniscus curvature, wherein
the control system is arranged to control the variable focus using
meniscus electrowetting forces.
7. A zoom optical system according to claim 6, wherein the fluid
meniscus lens further comprises a first electrode and a second,
different, electrode and the control system is arranged to apply a
voltage across said first and second meniscus electrodes to provide
said meniscus electrowetting forces.
8. A zoom optical system according to claim 1, wherein the lens
system comprises a solid lens capable of being arranged at varying
spatial positions relative to the switchable optical element.
9. A zoom optical system according to claim 1, wherein said lens
system comprises a liquid crystal lens having a varying optical
power.
10. Image capturing apparatus comprising a zoom optical system
according to claim 1, wherein with the optical system being in said
first mode, the apparatus is adapted to capture an image with a
first zoom setting, and with the optical system being in said
second mode, said apparatus is adapted to capture an image with a
second, different, zoom setting.
11. Image capturing apparatus according to claim 10, wherein said
image capturing apparatus further comprises a digital zoom system
arranged to introduce a digital zoom factor to an image captured in
the first mode and/or an image captured in the second mode.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a zoom optical system,
particularly but not exclusively for use in an image capturing
apparatus.
BACKGROUND OF THE INVENTION
[0002] Often when capturing an image of an object using an image
capturing apparatus, for example a camera, it is desirable to be
able to change a zoom setting for the image. With the distance
between the camera and the object remaining constant, a high zoom
factor allows an image of the object to be captured at a high level
of magnification and a narrow field of view. A low zoom factor
allows an image of the object to be captured at a low level of
magnification and a wide field of view. In the example of a camera
the high zoom factor is characteristic of a telephoto lens setting
and the low zoom factor is characteristic of a wide-angle lens
setting.
[0003] Different zoom factors require different effective focal
lengths of a zoom optical system. For a telephoto lens setting the
effective focal length is relatively long and for a wide-angle lens
setting the effective focal length is relatively short.
[0004] In order for images to be captured with different zoom
settings the effective focal length of a zoom optical system of the
camera must be variable whilst keeping the image of the object in
focus. Such a zoom optical system may be constructed using at least
two lenses which provide a variable focus.
[0005] A known zoom optical system comprises an array of solid
lenses which lie along a common light path. By varying positions of
these lenses along the light path, different effective focal
lengths can be obtained whilst keeping the image in focus, thus
allowing images having different zoom settings to be captured. Zoom
optical systems of this type are however relatively bulky and
mechanically complex. Movement of the different lenses may be
performed either manually or automatically, but these methods are
typically relatively expensive and lacking in robustness. The range
of zoom factors provided by such a zoom optical system depends on
parameters including the focal power of the individual lenses and
the distances between the lenses along the light path which can be
achieved. An increase in an upper limit of the zoom factor range of
a zoom optical system of this type will generally increase the bulk
and complexity of the zoom optical system.
[0006] Rather than one zoom optical system providing both a
telephoto and a wide-angle zoom function, it is often necessary to
swap the lenses of a camera between a telephoto and a wide-angle
system in order to obtain a range of different zoom factors. This
is a relatively slow and inconvenient process and requires a camera
user to carry different lenses in addition to the camera.
[0007] International patent application WO 03/069380 describes a
fluid meniscus lens. This lens comprises a fluid meniscus which
separates a first fluid and a second fluid and which has a
curvature. By varying this curvature it is possible to change the
focal length of the lens and the focus of an image. In applications
where the lens is to be used in various orientations, the fluids
are preferably density matched to avoid unwanted gravitational
effects. Therefore, two liquids, such as oil and water, which are
density matched are used.
[0008] Two such fluid meniscus lenses could be incorporated in a
zoom optical system in order to capture images having different
zoom factors. To achieve a large range in zoom factor requires a
large optical power change in each the fluid menisci. Since the
refractive indices of the two liquids are not greatly different,
and because the extent to which the curvature may be varied is
limited, the optical power range of the fluid meniscus lenses is
relatively small. This imposes a limit on the possible zoom factor
range provided by the zoom optical system. In particular, one lens
component in a zoom lens system (typically that closest the image
capture device) requires the greatest optical power range during
zooming, so the amount of zooming is constrained by the relatively
limited optical power range of the fluid meniscus lens used as that
one lens component.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a zoom
optical system having improvements to the zoom function for a
captured image whilst reducing the need for mechanical components
in the optical system.
[0010] In accordance with the present invention there is provided a
zoom optical system comprising a lens system which is arranged to
provide a variable zoom setting for a beam of radiation, wherein
the lens system comprises a switchable optical element having a
first mode and a second mode,
characterised in that the element including a first fluid, a second
fluid and a wavefront modifier having a part through which said
radiation beam is arranged to pass, wherein [0011] in the first
mode the switchable optical element has a first fluid configuration
in which said part is substantially covered by the first fluid, and
[0012] in the second mode the switchable optical element has a
second, different, fluid configuration in which said part is
substantially covered by the second fluid; and [0013] A zoom
optical system may be produced according to the present invention
which is relatively simple, compact, inexpensive and robust. The
zoom optical system preferably has a first effective focal length
in the first fluid configuration and a second effective focal
length in the second fluid configuration, wherein said first and
second effective focal lengths are each arranged to provide a
different zoom setting.
[0014] With the optical element being in the first mode, the lens
system has a first optical zoom setting. With the optical element
being in the second mode, the lens system has a second optical zoom
setting in which the zoom factor is increased.
[0015] The lens system preferably includes a first lens with a
continuously variable focus. The focus of the first lens may be
varied so that the image having either the first zoom setting or
the second zoom setting is correctly focused. When the switch
between the two zoom settings occurs, the first lens focus is also
altered stepwise to provide the correct zoom function. Consequently
the optical system. is a binary zoom optical system having two
discrete optical zoom settings.
[0016] A digital zoom function may be used in addition to provide
for additional zoom factors between the two zoom settings. In one
embodiment of the invention, an image capturing apparatus comprises
the optical system and comprises a digital zoom system arranged to
introduce a digital zoom factor to an image captured in the first
mode and/or an image captured in the second mode.
[0017] Preferably the switchable optical element in the first fluid
configuration is arranged to provide switchable electrowetting
forces by applying a first voltage across a first and second fluid
electrode, and in the second fluid configuration is arranged to
provide different switchable electrowetting forces by applying a
second, different, voltage across the first and a third fluid
electrode.
[0018] Preferably, the first fluid is a liquid and the second fluid
is gaseous. The term gaseous includes either of a gas mixed with a
vapour of a liquid, or only a gas. This is possible since the two
fluids do not need to be density matched, even if the device is to
be used in various orientations, and has the advantage that a
relatively large difference in refractive index between the two
fluids is provided.
[0019] The first lens may be in the form of a fluid meniscus lens.
In this embodiment, the switchable optical element preferably has a
maximum optical power range (between its two modes) which is
greater that the maximum optical power range of the first lens. By
this arrangement, the switchable optical element can be used as the
lens component requiring the greatest optical power range in the
lens system during zooming, so that the amount of zooming is not
constrained by the relatively limited optical power range of the
fluid meniscus lens.
[0020] Further features and advantages of the invention will become
apparent from the following description of preferred embodiments of
the invention, given by way of example only, which is made with
reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIGS. 1 to 3 show schematically a variable focus lens in
accordance with the prior art.
[0022] FIGS. 4 and 5 show a zoom optical system, not in accordance
with the present invention, comprising two fluid meniscus
lenses.
[0023] FIGS. 6 and 7 show schematic cross-sections, along lines A-A
and B-B respectively, of a switchable optical element in a first
fluid configuration, in accordance with the present invention.
[0024] FIGS. 8 and 9 show schematic cross-sections, along lines C-C
and D-D respectively, of the switchable optical element in a second
fluid configuration, in accordance with the present invention.
[0025] FIG. 10 shows schematically the optical system in a first
mode in accordance with an embodiment of the present invention.
[0026] FIG. 11 shows schematically a zoom optical system in a
second mode in accordance with an embodiment of the present
invention.
[0027] FIG. 12 shows schematically an image capturing apparatus
comprising a zoom optical system in accordance with an embodiment
of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0028] FIGS. 1 to 3 show, in accordance with the prior art, a
variable focus lens which is a fluid meniscus lens comprising a
cylindrical first meniscus electrode 2 forming a capillary tube,
sealed by means of a transparent front element 3 and a transparent
back element 4 to form a fluid chamber containing two different
fluids. The first meniscus electrode 2 may be a conducting coating
applied on the inner wall of a tube.
[0029] The two different fluids consist of two non-miscible liquids
in the form of an electrically insulating first liquid A, such as a
silicone oil or an alkane, referred to herein further as "the oil",
and an electrically conducting second liquid B, such as water
containing a salt solution. The two liquids are preferably arranged
to have an equal density, so that the shape of the meniscus can be
controlled independently of orientation, i.e. without dependence on
gravitational effects between the two liquids. This may be achieved
by appropriate selection of the first liquid constituent; for
example alkanes or silicone oils may be modified by addition of
molecular constituents to increase their density to match that of
the salt solution.
[0030] Depending on the choice of the oil used, the refractive
index of the oil may vary between 1.25 and 1.85. Likewise,
depending on the amount of salt added, the salt solution may vary
in refractive index between 1.33 and 1.60.The fluids are selected
such that the first fluid A has a higher refractive index than the
second fluid B.
[0031] The first meniscus electrode 2 is a cylinder of inner radius
typically between 1 mm and 20 mm. The first meniscus electrode 2 is
formed from a metallic material and is coated by an insulating
layer 5, formed for example of parylene. The insulating layer has a
thickness of between 50 nm and 100 .mu.m, with typical values
between 1 .mu.m and 10 .mu.m. The insulating layer is coated with a
fluid contact layer 6, which reduces the hysteresis in the contact
angle of the meniscus with the cylindrical wall of the fluid
chamber. The fluid contact layer is preferably formed from an
amorphous fluorocarbon such as Teflon.TM. AF1600 produced by
DuPont.TM.. The fluid contact layer 6 has a thickness of between 5
nm and 50 .mu.m. The AF1600 coating may be produced by successive
dip coating of the first meniscus electrode 2, which forms a
homogeneous layer of material of substantially uniform thickness
since the cylindrical sides of the first meniscus electrode 2 are
substantially parallel to the cylindrical electrode; dip coating is
performed by dipping the electrode whilst moving the electrode in
and out of the dipping solution along its axial direction. The
paralyne coating may be applied using chemical vapour deposition.
The wettability of the fluid contact layer by the second fluid is
substantially equal on both sides of the intersection of a meniscus
8 with the fluid contact layer 6 when no voltage is applied between
the first and a second meniscus electrode 7.
[0032] The second meniscus electrode 7 is annular and is arranged
at one end of the fluid chamber, in this case, adjacent the back
element. The second meniscus electrode 7 is arranged with at least
one part in the fluid chamber such that the electrode acts on the
second fluid B.
[0033] The two fluids A and B are non-miscible so as to tend to
separate into two fluid bodies separated by the fluid meniscus 8
having a curvature. When no voltage is applied between the first
and second meniscus electrodes, the fluid contact layer has a
higher wettability with respect to the first fluid A than the
second fluid B. Due to meniscus electrowetting forces, the
wettability by the second fluid B varies under the application of a
voltage between the first meniscus electrode 2 and the second
meniscus electrode 7, which tends to change the contact angle of
the meniscus at the three phase line (the line of contact between
the fluid contact layer 6 and the two liquids A and B). The
variable focus of the fluid meniscus lens comprises variations in
the fluid meniscus curvature which is variable in dependence on the
applied voltage.
[0034] Referring now to FIG. 1, when a low voltage V.sub.1, e.g.
between 0 V and 20 V, is applied between the meniscus electrodes
the meniscus adopts a first concave meniscus shape. In this
configuration, the initial contact angle .theta..sub.1 between the
meniscus and the fluid contact layer 6, measured in the fluid B, is
for example approximately 140.degree.. Due to the higher refractive
index of-the first fluid A than the second fluid B, the lens formed
by the meniscus, here called meniscus lens, has a relatively high
negative power in this configuration.
[0035] To reduce the concavity of the meniscus shape, a higher
magnitude of voltage is applied between the first and second
meniscus electrodes. Referring now to FIG. 2, when an intermediate
voltage V.sub.2, e.g. between 20 V and 150 V, depending on the
thickness of the insulating layer, is applied between the meniscus
electrodes the meniscus adopts a second concave meniscus shape
having a rate of curvature increased in comparison with the
meniscus in FIG. 1. In this configuration, the intermediate contact
angle .theta..sub.2 between the first fluid A and the fluid contact
layer 6 is for example approximately 100.degree.. Due to the higher
refractive index of the first fluid A than the second fluid B, the
meniscus lens in this configuration has a relatively low negative
power
[0036] To produce a convex meniscus shape, a yet higher magnitude
of voltage is applied between the first and second meniscus
electrodes. Referring now to FIG. 3, when a relatively high voltage
V.sub.3, e.g. 150 V to 200 V, is applied between the meniscus
electrodes the meniscus adopts a meniscus shape in which the
meniscus is convex. In this configuration, the maximum contact
angle .theta..sub.3 between the first fluid A and the fluid contact
layer 6 is for example approximately 60.degree.. Due to the higher
refractive index of the first fluid A than the second fluid B, the
meniscus lens in this configuration has a positive power.
[0037] Note that whilst achieving the configuration of FIG. 3 is
possible using a relatively high power, it is preferred that a
device including the lens as described is adapted to use only low
and intermediate powers in the ranges described, that is to say
that the voltage applied is restricted such that the electrical
field strength in the insulating layer is smaller than 20 V/.mu.m,
and excessive voltages causing charging of the fluid contact layer,
and hence degradation of the fluid contact layer, are not used.
[0038] Note furthermore that the initial, low voltage,
configuration will vary in dependence on the selection of the
liquids A and B, in dependence on their surface tensions). By
selecting an oil with a higher surface tension, and/or by adding a
component, such as ethylene glycol, to the salt solution which
reduces its surface tension, the initial contact angle can be
decreased; in this case the lens may adopt a low optical power
configuration corresponding to that shown in FIG. 2, and an
intermediate power configuration corresponding to that shown in
FIG. 3. In any case, the low power configuration remains such that
the meniscus is concave, and a relatively wide range of lens powers
can be produced without using an excessive voltage.
[0039] FIGS. 4 and 5 show a zoom optical system which could be
arranged to comprise two of the fluid meniscus lenses described
using FIGS. 1 to 3.
[0040] In the optical system shown a first fluid meniscus lens 9
and a second fluid meniscus lens 10 are arranged along an optical
axis OA. Also on the optical axis OA and between the first and the
second fluid meniscus lenses 9, 10 is a plurality of optical
elements 11 which aid a wavefront modification of a given radiation
beam travelling along the optical axis OA. The optical system is
arranged to capture an image of a given object which is an image
scene. An image detector 12 is arranged to detect an image of the
image scene following a focusing function and an introduction of a
zoom factor to the given radiation beam carrying the image by the
first and second fluid meniscus lenses 9, 10. In this example the
image detector 12 is a charged coupled device (CCD).
[0041] Referring to FIG. 4 showing the optical system at one limit
of the zoom range, and viewing along the optical axis OA, the
optical system has a first field of view .alpha..sub.1, the first
fluid meniscus lens 9 has a fluid meniscus 13 which is concave and
the second fluid meniscus lens 10 has a fluid meniscus 14 which is
concave. FIG. 4 illustrates a zoom setting, at a highest limit of a
zoom factor range of the optical system, introduced by the optical
system to a captured image of the image scene. The image is
captured by the CCD 12.
[0042] Referring to FIG. 5 and viewing along the optical axis OA
from the image scene which has a second field of view .alpha..sub.2
of a field of view to the CCD, the first fluid meniscus lens 9 has
a fluid meniscus 13 which is convex and the second fluid meniscus
lens 10 has a fluid meniscus 14 which convex. FIG. 5 illustrates a
zoom setting, at a lowest limit of the zoom factor range of the
optical system, introduced by the optical system to a captured
image of the object.
[0043] The zoom factor of the optical system shown in FIGS. 4 and 5
is limited. In a typical arrangement, the zoom factor at the
highest limit is approximately 2 times greater than that of the
image captured at the lowest zoom setting. Consequently the upper
limit in zoom factor difference is approximately two times, which
is relatively small.
[0044] Referring to FIGS. 6 to 7, a switchable optical element in
accordance with an embodiment of the present invention includes a
chamber 20, fluidly connected via two openings 22, 23 of the
chamber to a conduit 24 having two opposite ends. The first opening
22 of the chamber is fluidly connected to the first end of the
conduit and the second opening 23 of the chamber is fluidly
connected to the second end of the conduit so as to form a
fluid-tight enclosure for a fluid system. One side of the chamber
20 is enclosed by a wavefront modifier 26 with a part 28 having a
face exposed to the interior of the chamber 20. The wavefront
modifier is formed from a transparent material, for example
Zeonex.TM. which is a cyclo-olefin copolymer (COC) which is
non-soluble in aqueous liquids. This may for example be formed by
an injection moulding process. The face of the part 28 of the
wavefront modifier 26 is substantially aspherical and rotationally
symmetric about an optical axis OA.
[0045] The chamber 20 is further enclosed by a cover plate which
comprises a further wavefront modifier 36, which is formed from a
transparent material, similarly for example Zeonex.TM. and has a
different part 32. The different part 32 is covered in a
hydrophobic fluid contact layer which is transparent and formed for
example of Teflon.TM. AF1600 produced by DuPont.TM.. One surface of
this hydrophobic fluid contact layer is exposed to the interior of
the chamber 20.
[0046] The different part 32 has a face which is aspherical and
rotationally symmetric about the optical axis OA. The face of the
different part 32 has a differently aspherical curvature to an
aspherical curvature of the face of the part 28.
[0047] A given radiation beam travelling along the optical axis OA
is arranged to pass through the part 28 and the different part 32.
The wavefront modifier 26 is adapted to perform a first wavefront
modification and the further wavefront modifier 36 is adapted to
perform a second, different, wavefront modification on the given
radiation beam. The second wavefront modification is arranged to
complement the first wavefront modification.
[0048] A common, first fluid electrode 50 formed for example from a
metal, is located in the conduit 24 near to one opening 22 of the
chamber.
[0049] A second fluid electrode 34 lies between the cover plate 36
and the hydrophobic fluid contact layer. This second fluid
electrode 34 is formed as a sheet of a transparent electrically
conducting material, for example indium tin oxide (ITO). An
insulating layer (not shown), formed for example of parylene, may
be formed between the fluid contact layer and the second fluid
electrode 34. It is to be noted that the second electrode 34 has an
operative area which completely overlaps with the area occupied by
the face of the part 28 of the wavefront modifier 26. The
hydrophobic fluid contact layer has a surface area which completely
overlaps the face of the part 28 of the wavefront modifier.
[0050] The enclosed fluid system comprises a first fluid 44 and a
second fluid 46. The first fluid 44 comprises a polar and/or an
electrically conductive fluid. In this example the first fluid 44
is a liquid and is salted water, having a predetermined first
refractive index of approximately 1.37. The salted water has a
lower freezing point than that of non-salted water. The second
fluid in this example is preferably gaseous and comprises air which
has a second, different, refractive index of approximately 1. In
this example the air is mixed with a saturated vapour of the salted
water 44 and a refractive index difference between the refractive
index of the first fluid and the second fluid is approximately 0.4.
In a different example the first fluid 44 is an approximately 65%
by weight aqueous solution of KSCN having a refractive index of
approximately 1.49 and having a refractive index difference from
the second fluid 46 of approximately 0.5. In further examples where
the first fluid 44 is a polar organic liquid such as aniline or
anatabine, having a refractive index of approximately 1.59 or 1.57
respectively, the refractive index difference between the first
fluid and the second fluid is approximately 0.6. An advantage of
the second fluid being air is that if the switchable optical
element when manufactured is not air-tight, performance of the
element will not be substantially reduced. The first fluid 44 and
the second fluid 46 lie in contact with each other at two fluid
menisci 48, 49.
[0051] In a first fluid configuration of the switchable optical
element, as illustrated by FIGS. 6 and 7, the first fluid 44
substantially fills the chamber 20 and a portion of the conduit 24.
By substantially filling, it is meant that the first fluid 44
covers at least most of the part 28 of the wavefront modifier 26
and at least most of the different part 32 of the further wavefront
modifier 36. In this first fluid configuration, the first fluid
lies in contact with at least most of the exposed surface of the
hydrophobic fluid contact layer in the chamber. The first fluid
electrode 50 lies in contact with the portion of the conduit filled
by the first fluid 44.
[0052] The conduit 24 is formed between conduit walls 41 and a
conduit cover plate 42. The conduit cover plate is covered by a
hydrophobic fluid contact layer 38 exposed on one surface to the
interior of the conduit 24, the hydrophobic fluid contact layer
being formed for example of AF1600.TM.. A third fluid electrode 40
lies between the conduit cover plate 42 and the hydrophobic fluid
contact layer 38. This electrode is formed from an electrically
conductive material, for example indium tin oxide (ITO). It is to
be noted that the third fluid electrode 40 has a surface area which
overlaps with most of the interior of the conduit 24.
[0053] In the first fluid configuration of the element, the second
fluid 46 substantially fills the conduit 24 except for the portion
filled by the first fluid 44 which is in contact with the common,
first fluid electrode 50.
[0054] In a second fluid configuration of the switchable optical
element, as illustrated by FIGS. 8 and 9, the first fluid 44
substantially fills the conduit 24. In this second fluid
configuration the first fluid 44 continues to lie in contact with
the common first fluid electrowetting electrode 50 located in the
previously described portion of the conduit. The first fluid 44 now
lies in contact with the hydrophobic fluid contact layer 38 of the
conduit. The second fluid 46 now substantially fills the chamber 20
such that the second fluid 46 covers at least most of the part 28
of the wavefront modifier 26 and at least most of the different
part 32 of the further wavefront modifier 36. Additionally a
portion of the conduit 24 is filled by the second fluid 46. This
portion of the conduit 24 is at the opposite end to the portion in
which the common, first fluid electrode 50 is located. In the
second fluid configuration the first fluid electrode 50 lies in
contact with the first fluid 44 which fills the portion of the
conduit 24.
[0055] A fluid switching system (not shown) is connected to the
common first fluid electrode, the second fluid electrode and the
third fluid electrode. The fluid switching system acts upon the
switchable optical element and is arranged to switch the first and
the second fluid configurations. In the first fluid configuration
the fluid switching system is arranged to apply a voltage V.sub.1
of an appropriate value across the common, first fluid electrode 50
and the second fluid electrode 34. The applied voltage V.sub.1
provides switchable electrowetting forces such that the switchable
optical element of the present invention tends to adopt the first
fluid configuration wherein the electrically conductive first fluid
44, moves to substantially fill the chamber 20. As a result of the
applied voltage V.sub.1, the hydrophobic fluid contact layer of the
chamber 20 temporarily becomes at least relatively hydrophilic in
nature, thus aiding the preference of the first fluid 44 to
substantially fill the chamber 20. It is envisaged that whilst in
the first fluid configuration, no voltage is applied across the
common, first electrode 50 and the third electrowetting electrode
40, such that the fluid contact layer in the conduit remains
relatively highly hydrophobic.
[0056] In order to switch between the first fluid configuration and
the second fluid configuration of the switchable optical element,
the fluid switching system switches off the applied voltage V.sub.1
and applies a second applied voltage V.sub.2 of an appropriate
value across the common, first fluid electrode 50 and the third
fluid electrode 40. No voltage is applied across the common, first
fluid electrode 50 and the second fluid electrode 34.
[0057] The switchable optical element now lies in the second fluid
configuration state, in which the first fluid 44 substantially
fills the conduit 24 as a result of switchable electrowetting
forces provided by the applied voltage V.sub.2. With the applied
voltage V.sub.2 the hydrophobic fluid contact layer 38 of the
conduit 24 is now at least relatively hydrophilic and tends to
attract the first fluid 44. The first fluid 44 moves to fill the
portion of the conduit 24 in which the common first fluid electrode
50 is located. As earlier described, the second fluid 46 now
substantially fills the chamber 20. The hydrophobic fluid contact
layer of the chamber 20 is now relatively highly hydrophobic and
aids this arranging of the second fluid in the second fluid
configuration.
[0058] During the transition between the first and the second fluid
configurations of the element, as controlled by the fluid switching
system, the first and second fluids 44, 46 of the fluid system flow
in a circulatory manner through the fluid system, each of the
fluids displacing each other. In this circulatory fluid flow during
the transition from the first to the second fluid configuration,
the first fluid 44 passes out of the chamber 20 into one end of the
conduit 24 via one opening 22 of the chamber. Simultaneously the
second fluid 46 passes from the other end of the conduit 24 into
the chamber 20 via the other opening 23 of the chamber. During the
transition, from the second to the first fluid configuration, an
opposite circulatory fluid flow occurs.
[0059] Thus, when changing from the first fluid configuration to
the second fluid configuration, the applied voltage V.sub.2 across
the third fluid electrode 40 and the common, first fluid electrode
50 attracts the electrically conductive first fluid 44 into the
chamber 20, thus displacing the electrically insulating second
fluid 46 out of the chamber 20. Additionally, the hydrophobic fluid
contact layer 32 of the chamber 20 repels the electrically
conductive first fluid 44 out of the chamber 20 into the conduit
24. The transition from the second to the first fluid configuration
is the reverse of the transition from the first to the second
transition state in these terms.
[0060] FIG. 10 and FIG. 11 shows schematically a binary zoom
optical system used in a camera in accordance with an embodiment of
the present invention. FIG. 10 shows the optical system when in a
first zoom mode and FIG. 11 shows the optical system when in a
second, different zoom mode.
[0061] The binary zoom optical system comprises a first lens which
is arranged to provide a continuously variable focus for a given
radiation beam travelling along an optical axis OA. In this
embodiment the first lens is a fluid meniscus lens 52 which is
similar to that described using FIGS. 1 to 3. The binary zoom
optical system further comprises a switchable optical element 54
which is similar to that described using FIGS. 6 to 9, and a fluid
switching system 56 which is similar to that described earlier for
switching the first and second configuration. Elements and features
of the fluid meniscus lens 52, the switchable optical element 54
and the fluid switching system 56 are similar to those described
previously. For such elements and features, similar reference
numerals will be used herein, incremented with 100; corresponding
descriptions should be taken to apply here also. The face of the
part 128 (not indicated) and the face of the different part 132
(not indicated) are both aspherical and are arranged to provide the
binary zoom optical system with an improved quality field of view
of an object which has a minimised periphery distortion of a
captured image of the object.
[0062] Arranged on the optical axis OA and lying between the fluid
meniscus lens 52 and the switchable optical element 54 is a solid
lens group including two solid lenses 58, 60 adjacent the
switchable optical element 54 and adjacent the fluid meniscus lens
52. Between the two solid lenses is an optical stop (not shown).
One or both of the solid lenses of the solid lens group 58 have a
refractive index similar to the refractive index of the first fluid
144 of the switchable optical element 54. The binary zoom optical
system is arranged to capture an image of a given object which is
an image scene. An image detector 62, for example a charged coupled
device (CCD), is arranged to detect and capture an image of the
image scene at the optical zoom setting provided by the fluid
meniscus lens 52 and the switchable optical element 54 to the given
radiation beam carrying the image. In this embodiment the
switchable optical element 54 is arranged between the fluid
meniscus lens 52 and the image detector 62 and has a maximum
optical power range (between its two modes) which is greater that
the maximum optical power range of the fluid meniscus lens 52.
[0063] Referring to FIG. 10, the binary zoom optical system is in
the first zoom mode with the switchable optical element 54 being in
the first fluid configuration. In the first fluid configuration the
binary zoom optical system has a relatively long first effective
focal length which is arranged to provide a relatively high zoom
factor. On viewing along the optical axis OA from the fluid
meniscus lens 52 to the switchable optical element 54, the fluid
meniscus 108 has a concave curvature. In the first zoom mode the
optical system has a third field of view .alpha..sub.3
corresponding to a relatively high zoom factor provided by the
switchable optical element 54 in the first zoom mode.
[0064] Referring to FIG. 11, the binary zoom optical system is in
the second zoom mode with the switchable optical element 54 being
in the second fluid configuration. The fluid switching system 56
switches the first fluid configuration to the second fluid
configuration in a similar manner to that described earlier using
FIGS. 6 to 9. In the second fluid configuration the switchable
optical element 54 has a relatively short second effective focal
length which is arranged to provide a relatively low zoom setting.
The second effective focal length is shorter than the first
effective focal length. On viewing along the optical axis OA from
the fluid meniscus lens 52 to the switchable optical element 54,
the fluid meniscus 108 has a convex curvature. The binary zoom
optical system further comprises a control system 64 which is
connected to the first and second meniscus electrodes and is
arranged to apply a voltage across the first and second meniscus
electrodes in order to control the variable focus by varying the
curvature of the fluid meniscus 108 using electrowetting
forces.
[0065] In the second zoom mode, the optical system has a fourth
field of view .alpha..sub.4. The fourth field of view .alpha..sub.4
of the image captured in the second zoom mode in this example is
greater than the third field of view .alpha..sub.3 of the image
captured in the first zoom mode. Preferably, the optical zoom
factor between the two modes is greater than 2, and more preferably
greater than 3.
[0066] With the binary zoom optical system being in either the
first zoom mode or the second zoom mode the variable focus may be
varied by the control system 62 applying a different voltage across
the first and the second meniscus electrodes to vary the curvature
of the fluid meniscus 108. The curvature may be varied such that it
is, at one limit of its power range, convex and, at the other limit
of its power range, concave.
[0067] FIG. 12 shows schematically an image capturing apparatus 66
comprising a binary zoom optical system 68 which is similar to the
binary zoom optical system of an embodiment of the present
invention described previously. Elements and features of the binary
zoom optical system 68 are similar to those described before. For
such elements and features, similar reference numerals will be used
herein, incremented with 200; corresponding descriptions should be
taken to apply here also. The image capturing apparatus in this
embodiment is a camera and is arranged to record an image of a
given object which is an image scene including the feature 70. An
apparatus control system 72 is arranged to control functioning of
the camera and is connected to the control system 264, the fluid
switching system 256, a power supply 74, an image display system
76, an image storage system 78 and a user control system 80. The
apparatus control system comprises an image modification system
82.
[0068] In operation a user controls a functioning of the camera
using the user control system 80. The user is able to select the
first zoom mode or the second zoom mode of the binary zoom optical
system 68. The apparatus control system 72 controls the fluid
switching system 256 so that, as described previously, either the
first fluid configuration is selected in the first zoom mode or the
second fluid configuration is selected in the second zoom mode. In
the camera the first zoom mode is a telephoto zoom mode having a
relatively narrow field of view of the image scene and the second
zoom mode is a wide-angle zoom mode having a relatively wide field
of view of the image scene. Whilst pointing the camera
appropriately at the image scene so that the binary zoom optical
system 68 may correctly record the image and with the camera in
either the telephoto zoom mode or the wide-angle zoom mode, the
user views the image display system 76 and selects a specific zoom
factor of the image of the image scene to be recorded. In doing so
the apparatus control system 72 controls the control system 264
which appropriately varies the curvature of the fluid meniscus as
described previously.
[0069] The binary zoom optical system allows a relatively high zoom
setting for the image to be recorded to be selected with the camera
being in the telephoto zoom mode, or a relatively low zoom setting
with the camera being in the wide-angle zoom mode. The image
modification system 82 is a digital zoom system which is arranged
to introduce a variable digital zoom factor to an image captured in
the telephoto zoom mode or the wide-angle zoom mode such that
further zoom settings may be obtained. This digital zoom factor is
introduced, for example to an image captured in the wide-angle zoom
mode with the relatively low, or to an image captured in the
telephoto zoom mode with the relatively high zoom factor. This
allows an image to be recorded which has a zoom setting between the
relatively low zoom setting and the relatively high zoom setting.
The digital zoom system 82 is also able to introduce a variable
digital zoom factor to an image recorded in the telephoto mode and
with the relatively high zoom factor. This allows an image to be
recorded which has a zoom setting which is higher than the optical
zoom setting of the telephoto zoom mode.
[0070] In embodiments of the present invention described previously
the binary zoom optical system comprises a lens which is arranged
to provide a continuously variable focus and is a fluid meniscus
lens. In a different embodiment of the present invention the lens
which is arranged to provide the continuously variable focus is a
solid lens. The lens is arranged to be moved to different spatial
positions relative to the switchable optical element along the
optical axis OA. The lens itself has a fixed focal power. An
alternative control system to that described earlier and comprised
by the binary zoom optical system is arranged to control the
variable focus continuously by varying the spatial positions of the
lens. Different spatial positions are obtained by for example a
motor driving a geared system to move the lens along the optical
axis OA. By the control system appropriately varying the spatial
position of the lens on the optical axis OA, it is possible to vary
a focal power and a zoom factor, similarly to that previously
described, of an image of a given object captured by the binary
optical system.
[0071] It is envisaged that, in alternative embodiments of the
invention, the lens array comprises a plurality of solid lenses
which can independently be moved to different spatial positions
along the optical axis OA using mechanical actuators.
[0072] In further alternative embodiments of the invention, the
lens which is arranged to provide the continuously variable focus
is a liquid crystal lens, which obviates the need for a mechanical
system to move lens components.
[0073] It is further envisaged that the different fluids of the
fluid meniscus lens and the switchable optical element may be
different to those described and may each have a different
refractive index. It is also envisaged that the first fluid and the
second fluid of the switchable optical element may alternatively be
gaseous and a liquid respectively, or that the first and second
fluids are both liquids.
[0074] It is envisaged also that materials from which elements, for
example the wavefront modifiers and the electrodes, of the binary
zoom optical system are formed may be different to those described.
Different materials may be selected according to certain
properties, for example a wavefront modifier material of the
switchable optical element must not be soluble in the first fluid
or the second fluid.
[0075] It is further envisaged that the face of the part and/or the
different part of the switchable optical element has a different
aspherical shape or are alternatively spherical. It is additionally
envisaged that the face of the part or different part may comprise
a non-periodic structure (NPS) or a diffraction grating.
[0076] The switchable optical element described operates in a
circulatory manner through the fluid system. It is envisaged that
alternative constructions of the switchable optical element in
relation to an arrangement and fluid flow during a fluid
configuration transition of the first fluid and the second fluid
may be used, for example non-circulatory fluid flow between the
main chamber and one or more fluid reservoirs may be used.
[0077] It is envisaged in alternative embodiments that the
switchable optical element described is differently constructed and
that the wavefront modifier comprises a further fluid electrode
similar to the second fluid electrode of the cover plate comprising
the further wavefront modifier. The further fluid electrode is
electrically connected to the second fluid electrode such that the
applied voltage V.sub.1 is applied across the common first fluid
electrode, the second fluid electrode and the further fluid
electrode in the first fluid configuration. It is additionally
envisaged that the part of the wavefront modifier is covered in a
hydrophobic fluid contact layer formed for example of Teflon.TM.
AF1600. One surface of this layer is exposed to the interior of the
chamber. In this envisaged embodiment the construction of the
switchable optical element allows a more efficient movement of
fluid between the chamber and the conduit during switching between
the first and the second fluid configuration.
[0078] In different possible embodiments of the switchable optical
element, the fluid switching system may be differently arranged to
switch between the first and the second fluid configurations using
mechanisms which do not involve electrowetting forces, for example
a mechanical pumping mechanism.
[0079] Note further that a conventional zoom optical system
comprising an array of lenses may be combined with the binary zoom
optical system of the present invention to allow images to be
captured having further different zoom settings.
[0080] The binary zoom optical system of the present invention is
described for inclusion and operation in an image capturing
apparatus such as a camera. Inclusion of the binary zoom optical
system in various image capturing devices is envisaged, for example
a mobile telephone which includes a camera, or other devices which
include a camera. The above embodiments are to be understood as
illustrative examples of the invention. Further embodiments of the
invention are envisaged. It is to be understood that any feature
described in relation to any one embodiment may be used alone, or
in combination with other features described, and may also be used
in combination with one or more features of any other of the
embodiments, or any combination of any other of the embodiments.
Furthermore, equivalents and modifications not described above may
also be employed without departing from the scope of the invention,
which is defined in the accompanying claims.
* * * * *